Refining apparatus, chiefly for screening paper pulp

ABSTRACT

A perforated screen associated with the conventional blades the movement of which over the screen removes the impurities collecting on the perforations. To reduce the component of the speed of the fluid in parallel with the surface of the screen, hindrances constituted by parallel recesses or by parallel blades are provided in substantial parallelism with the blades across the screen surface facing the blades; said hindrances may be continuous or arranged in staggered formation.

United States Patent Inventor Pierre Lamort Vitry-le-Francois, France Appl. No. 747,503 Filed July 25, 1968 Patented Nov. 2, 1971 Assignee Etablissements E & M Lamort Fils Vitry-le-Francois, Marne, France Priority Aug. 2, 1967 France 116,590

REFINING APPARATUS, CHIEFLY FOR SCREENING PAPER PULP 9 Claims, 9 Drawing Figs.

U.S. Cl. 241/88, 209/393, 241/90 Int. Cl. ..B02c 13/ 13, B02c 13/14, B07b l/00 Field ofSearch 24l/88,90, 74, 46.06, 46.08, 46.11; 209/265, 267, 283, 393, 395, 399

[56] References Cited UNITED STATES PATENTS 2,225,095 12/1940 Beverly 241/88 3,380,669 4/1968 Hatton 241/90 X 2,833,484 5/1958 Gooding..'.... 241/188 3,409,132 11/1968 Meadows 209/393 X FOREIGN PATENTS 1,049,477 8/1953 France 241/88 Primary Examiner-Donald G. Kelly Attorney-Michael S. Striker Mill/171 PATENTEDYNUV, 2 1911 3,517. 008

' sum 10F 2 F7 .IPR/ORAAT m 1QMMQQ Fig? 2 PRIOR ART 5 A villi/Ill PATENT EBmJv 2 ml sum 2 OF 2 Fun-urn PIER are under REFINING APPARATUS, CIIIEFLY FOR SCREENING PAPER PULP The present invention has for its object improvements in refining apparatus of the type adapted to screen under pressure certain material, such as in particular paper pulp and generally speaking includes a cylindrical screen housed inside a vat and provided with slots or ports which are maintained in clean condition by pulses generated by blades moving in the vicinity of said screen. Such blades may be located either on the upstream side of the screen, that is within the pulp which has not yet been screened, or else on the downstream side of the screen, within the screened pulp. In both cases the proper operation of the apparatus depends on the behavior of the fibers incorporated in the pulp, with reference to the perforation in the screen.

Certain difficulties are often met in connection with slotted screens, but also in other types of screens. For instance, in refining apparatus provided with blades on the upstream side of the screen, assuming the slots are arranged in parallelism with the blades, the fibers engage said slots perpendicularly thereto since they lie longitudinally in parallelism with the flow of the liquid which is carried along by the blades. If the length of the fibers is larger than the breadth of the slots, they cannot pass through the latter and clog them gradually. If in contradistinction the slots are perpendicular to the blades, the fibers engage the slots in the direction thereof and pass easily through them, but by reason of the high speed at which the blades drive the liquid, there is a cramming at the ends of the slots and the fibers collect gradually so that the slots are finally completely clogged. In the case of refining apparatus provided with blades on the downstream side of the screen, the movement of the blades produces a return flow of a certain amount of liquid through the slots, which releases them of any clogging material. Now, under the action of the blades, the liquid progresses on the downstream side of the screen at a speed having a high component of movement along a line parallel with said screen and this disturbs the return flow of the liquid ifthe slots are parallel with said blades, or else leads to a cramming of fibers inside the ends of the slots if the latter are perpendicular to the blades.

A further difficulty which is often met consists in that the paper pulp frequently carries impure particles appearing as filaments which under the action of the eddying liquid are entangled and form actual cords or strings which may form a wedge between the blades and the screen and lead to a stoppage of the apparatus.

The present invention has for its object to eliminate the above mentioned difficulties and it covers at least one of the following features, considered separately or in any suitable combination:

the screen provided with flow impediments distributed at different points of the surface of the screen facing the blades, said flow impediments being arranged in parallelism with or with a slight obliquity relative to said blades and having for their object to cut off the component of movement parallel with the surface of the screen,

the flow impediments are constituted by elongated recesses extending in parallelism with or with a slight obliquity relative to the blades, and recesses being cut in the surface of the metal sheet forming the screen and extending between the perforations of said screen,

the flow impediments are constituted by bars extending in parallelism with or with a slight obliquity relative to the blades, said bars being secured to the metal sheet forming the screen,

each of the flow impediments extends throughout the height of the screen, while a number of perforations constituted by holes or slots are arranged between any two parallel flow impediments,

the flow impediments are arranged in staggered formation on the screen,

the screen is provided with slots perpendicular to the blades, while the flow impediments are arranged adjacent the downstream ends of said slots,

the screen is provided with slots parallel with the blades while the flow impediments, one for each slot, are arranged right on the downstream rim of each slot,

the bars referred to form cutters the severing edges of which are almost in contact with the blades, so that any filamentshaped impurities which may engage the leading edges of said blades are severed by said edges.

By way of example and with a view to furthering the understanding of the invention, the accompanying drawings include:

in FIG. 1 a diagrammatic view of a conventional refining apparatus according to prior art, the slots in which are parallel with the blades;

in FIG. 2 a diagrammatic view of a conventional refining apparatus according to prior art, the slots in which are perpendicular to the blades;

in FIG. 3 a diagrammatic view of a refining apparatus according to the invention, wherein the slots are parallel with the blades and associated with flow impediments according to the invention;

in FIG. 4 a diagrammatic view of a refining apparatus the slots in which are perpendicular to the blades and associated with flow impediments according to the invention;

in FIG. 5 a diagrammatic view on a larger scale of a detail which may be incorporated with the refining apparatus according to the invention; I

in FIG. 6 a diagrammatic view of a modified embodiment; and in FIGS. 7-9 diagrammatic views of further modifications. Turning to FIG. 1, there is illustrated an embodiment wherein as in the other figures the blades 1 are arranged ahead of the screen 2; the fibers 4 are shown in FIG. 1 as extending trans versely across the narrow input ends 312 of the slots, which latter open at their output ends 3a so as to form diffusers on the downstream face of the screen plate or sheet, the fibers being thus urged over the slot edges by the stream of liquid passing through said slots in the direction indicated by the arrows. The blades 1, which have a hydrodynamic outline, progress at a high speed across the slots 3 and produce a certain return flow by reason of their negative angle of incidence, but they increase at the same time the speed of the liquid in a direction parallel with the screen,- so that the fibers 4 retain the general transverse direction illustrated which objectionably disturbs the operation of the apparatus. In the case of FIG. 2, the slots 3 are perpendicular to the blades 1 and the fibers 4 have a tendency to collect at the ends of the slots 3. Both FIGS. 1 and 2 illustrate constructions known from the prior art.

In order to eliminate the drawbacks of the conventional apparatus in FIGS. 1 and 2, the invention provides flow impedi ments constituted by small bars 5 (FIGS. 3 to 5) arranged with a predetermined spacing on the surface of the screen 2 facing the blades 1 and in parallelism with the latter, so that the component of the speed of the liquid which is parallel with the screen 2 is cut off in the vicinity of said screen. The bars 5 may extend as continuous members or else they may consist of sections arranged in staggered relationship as shown in FIG. 7.

In the case where the slots 3 are perpendicular to the blades 1, as illustrated in FIG. 4, the bars 5 are located in registry with the ends of the slots 3, so as to eliminate as far as possible the risk of a cramming of the fibers in said slots.

The bars 5 may be arranged either in parallelism with the blades 1 or they may be arranged slightly sloping with reference thereto, so as to constrain the impurities stopped by the screen to move towards the output provided at the ends of the bars for recovering such impurities.

Depending upon the circumstances of a given case, there are one or more slots 3 provided in the area separating two successive flow impediments parallel therewith.

According to a further embodiment of the flow impediments illustrated in FIGS. 8 and 9, the latter may be constituted by recesses 5' which are elongated and cut in the actual screen 2 at the side thereof at which the blade I is located.

According to a still further feature of the invention the bars 5 may be provided with a severing edge 50, as illustrated in FIG. 5, the size of which is such that the blades pass very near the severing edge thus obtained. If a filamentary cord or string of fibers has a tendency to engage the cutting edge of a blade I, it is immediately cut off and released when said blade 1 passes in front of the severing edge 5a. This prevents any fibrous cord from increasing in size and gathering over the blades 1.

When the slots are parallel with the blades, there is provided one flow impediment for every slot right on the downstream rim on each slot, in order to increase to a maximum their cleaning effect and that specially if they are situated opposite to the downstream side of the screen. This is illustrated in FIG. 6.

Iclairn:

I. In a pulp screening apparatus, the combination comprising a screen extending in a first direction and being provided with perforations therethrough for the passage of a fiber-containing liquid through said perforations, said screen having an upstream side and a downstream side; first means movable substantially parallel to said screen on one side of the latter through the fiber-containing liquid for imparting to the liquid a primary component of movement in said first direction and a secondary component of movement in a second direction transversely of said first direction; and second means stationarily arranged relative to said screen in the region of said perforations at said one side of said screen at which said first means is located and projecting beyond said one side of said screen in direction toward said first means and being operative for counteracting said primary component of movement imparted to the liquid by said first means as it passes through the liquid in a region of said one side of said screen so that said liquid retains in said region substantially only said secondary component of movement.

2. In an apparatus as defined in claim I, wherein said first means comprise at least one blade with a profile of hydrodynamic configuration mounted proximal to said one side of said screen for movement in a plane substantially parallel to said one side.

3. In an apparatus as defined in claim 1, wherein said one side is said upstream side of said screen.

4. In an apparatus as defined in claim I, wherein said one side is said downstream side of said screen.

5. In an apparatus as defined in claim I, wherein said second means comprises a plurality of spaced elongated recesses provided in said one side of said screen in parallelism with one another.

6. In an apparatus as defined in claim I, wherein said second means comprises a plurality of spaced elongated parallel bars rigid with said screen at said one side thereof.

7. In an apparatus as defined in claim 1, said second means comprising a plurality of discrete elements distributed in staggered formation over said one side of said screen.

8. In an apparatus as defined in claim 3, said first means comprising at least one blade mounted proximal to said one side of said screen for movement substantially parallel to said one side, and said second means comprising a plurality of elongated bars rigid with said one side extending transversely of said secondary component of movement and having respective cutting edges close to said blade so that solid impurities which adhere to the leading edge of said blade are severed when said leading edge moves past the respective cutting edges.

9. In an apparatus as defined in claim 1, wherein said per forations are constituted by a plurality of substantially parallel slots for passage of the liquid therethrough, and wherein said second means comprise a plurality of elongated elements extending transversely of said slots at the ends of the same which trail in the direction of said primary component of said stream. 

2. In an apparatus as defined in claim 1, wherein said first means comprise at least one blade with a profile of hydrodynamic configuration mounted proximal to said one side of said screen for movement in a plane substantially parallel to said one side.
 3. In an apparatus as defined in claim 1, wherein said one side is said upstream side of said screen.
 4. In an apparatus as defined in claim 1, wherein said one side is said downstream side of said screen.
 5. In an apparatus as defined in claim 1, wherein said second means comprises a plurality of spaced elongated recesses provided in said one side of said screen in parallelism with one another.
 6. In an apparatus as defined in claim 1, wherein said second means comprises a plurality of spaceD elongated parallel bars rigid with said screen at said one side thereof.
 7. In an apparatus as defined in claim 1, said second means comprising a plurality of discrete elements distributed in staggered formation over said one side of said screen.
 8. In an apparatus as defined in claim 3, said first means comprising at least one blade mounted proximal to said one side of said screen for movement substantially parallel to said one side, and said second means comprising a plurality of elongated bars rigid with said one side extending transversely of said secondary component of movement and having respective cutting edges close to said blade so that solid impurities which adhere to the leading edge of said blade are severed when said leading edge moves past the respective cutting edges.
 9. In an apparatus as defined in claim 1, wherein said perforations are constituted by a plurality of substantially parallel slots for passage of the liquid therethrough, and wherein said second means comprise a plurality of elongated elements extending transversely of said slots at the ends of the same which trail in the direction of said primary component of said stream. 